What is Acid Detergent Fiber (ADF) in Horse Hay?

Having your hay analyzed is a great idea. It is the only way to determine the actual nutrient content of your hay. It is important to know this so that you can be sure your horse is consuming an adequate diet. You may or may not need to feed grain depending on the quality of your hay. The better the quality of the hay you feed, the less grain you will need to feed. This can be a significant savings.

When discussing hay quality or looking at your hay sample analysis results the acronym ADF is often heard or seen. ADF stands for Acid Detergent Fiber and is the percentage of the plant material in the forage that is difficult for your horse to digest. This indigestible part contains cellulose, lignin, and silica.

Basically ADF is a measure of the fiber concentration of the hay, shown as a percent. As ADF increases, digestibility and nutrient availability decreases. It’s what makes hay “stemmy” and provides low nutritional value. So ADF is negatively correlated with overall digestibility.ADF is a useful gauge of the quality of the hay and of the energy and digestibility of it. Low ADF values mean higher energy value and digestibility; therefore low ADF values are desirable. In fact, all of the energy estimates presently used in forage testing are calculated from ADF alone.

The other factor to look for on your hay analysis is NDF or Neutral Detergent Fiber. This is a measure of the plant’s cell wall content in the hay. NDF measures hemicellulose, cellulose and lignin representing the fibrous bulk of the forage. These three components are classified as cell wall or structural carbohydrates. Much like a skeleton in an animal, they give the plant support as it grows.

This is another value where a higher value is not better. The higher the NDF value is the less the horse will be able to eat of the hay. So basically NDF measures forage intake potential. If you see left over, wasted hay this could be an indicator of a high NDF. Good hay has low NDF as horses can and will eat every last bit.

High quality forages are considered to have an ADF of 25 to 45% and NDF of 35 to 55% (as fed). Lower quality forages are considered to have an ADF of 35 to 45% and NDF of 55 to 70% (as fed).

Here is a hay analysis report for you to see how these values affect the Relative Feed Value (RDF) of the hay:

This chart is a nice reference for what you should look for in quality hay:

Hopefully, in the future hay producers will all get their hay tested and now, after this post, you will know how to read it!